1. Field of the Invention
This invention relates to an ultrasonic transmitter-receiver using a laminated piezo-electric element, and more particularly to an ultrasonic transmitter-receiver with improved sensitivity characteristics and improved pulse characteristics (transition characteristics).
2. Description of the Prior Art
Conventional ultrasonic transmitter-receivers used in the air usually include laminated piezo-electric ceramic elements and the laminated elements are designed to work at resonance or anit-resonance points of flexible oscillation. Further, because of the mechanical impedance of the air being substantially smaller than that of the piezo-electric ceramic element, the laminated element is bonded to a diaphragm in an attempt to reduce mechanical impedance.
Structure and operating properties of the conventional ultrasonic transmitter-receiver are illustrated in FIGS. 1 and 2.
As indicated in FIG. 1, an end of a coupling shaft 2 is fixed to pass through a central portion of a laminated piezo-electric elements 1 with the remaining end thereof being secured fixedly on a diaphragm 3. Nodes of oscillation of the laminated piezo-electric element 1 are mounted via a flexible adhesive 5 on tips of supports 4. There is further provided terminals 6 and 6', a housing 7 for protecting the laminated piezo-electric element 1 and so forth against the outside atmosphere, a protective mesh 8 disposed at a top portion of the housing 7 and lead wires 9 and 9' for connecting electrically the laminated piezo-electric element 1 to the terminals 6 and 6'.
FIG. 2 depicts the waveform of radiations transmitted when the ultrasonic transmitter-receiver of the above mentioned structure operates over a plurality of pulses, wherein rise time and fall time are relatively long, i.e. on the order of 2 milliseconds.
In the case where it is necessary to provide readouts within a short period of time through the use of the conventional ultrasonic transmitter-receiver, a particular signal is sometimes received before the preceding signal is received by the receiver because of the longer rise and fall times of the latter, thus making measurements inaccurate.
Furthermore, in the case where transmission and reception of ultrasonic radiations are performed with a single unit element, it takes a substantial amount of time to make the element ready to receive the signals after transmission of the signals. Of course, readouts are not available until the element is made ready to receive the signals.
The present invention is intended to provide a resolution to the above discussed problems.